The present invention relates generally to a device for measuring strain parameters of a generally cylindrical member and, more particularly, to such a device which is adapted for measuring such parameters in a generally cylindrical member of virtually any size.
Engineers and technicians often need to secure one or more strain gages to a valve stem, drive shaft or other generally cylindrical member for the purpose of measuring axial and/or circumferential strain for ascertaining axial force, as well as to measure torsional strain for ascertaining torque on the member. If bending of the cylindrical member could be occurring while measuring the axial strain, strain gage elements must be affixed to opposite sides of the cylindrical member in order to cancel out any such bending effects. Having all of the necessary strain gage elements located on a single supporting grid prior to bonding to the cylindrical member is desirable for proper positioning of the strain gage elements on opposite sides and for proper alignment of the strain gage elements themselves. However, the use of a single supporting grid for all of the strain gage elements generally means that a different size grid must be fabricated to accommodate each of the various sizes of the cylindrical members for which strain parameters may be measured. The use of such multiple size grids can be bothersome and very costly from a production and stocking standpoint when cylindrical members of many different diameters may have to be strain gaged.
The present invention overcomes the requirement of having to use a different size supporting grid for measuring strain parameters of each different diameter stem, shaft or other cylindrical member, while still retaining the important strain gage alignment features available when using a single supporting grid. The desired result is accomplished by effectively separating the supporting grid into two individual parts, called holders, with each holder having its own properly aligned strain gage elements and by utilizing a precisely fitting tensioning band to assure precise alignment between the two holders on the cylindrical member. The tensioning band also provides a way of securely clamping each strain gage substrate to the stem, shaft, or other cylindrical member during the gage affixing process. Preferably, electrical connections between the gage elements of the two holders are prewired to a standard connector as part of an assembly so that contact resistance does not adversely effect performance.